The invention relates to a direct current electric motor, and more particularly relates to an arrangement of a permanent magnet and an armature of the motor in which the permanent magnet has a plurality of N-magnetic poles and a plurality of S-magnetic poles, each pole defining a magnetic range of its own and the armature is composed of a first phase coil and a second phase coil each including a plurality of groups of conductors, the conductors in each group being extended substantially in prallel with each other, instead of being bundled together, each group of conductors of the first phase coil and each group of conductors of the second phase coil being alternately arranged adjacent to each other, one being disposed in one half of the magnetic range of the permanent magnet and the other being disposed in the other half of the magnetic range, so as to produce a constant torque in each half of the magnetic range. In this connection, the conductors of the first and second phase coils are wholly utilized to produce a constant torque in each half of the magnetic range for smoothly driving the motor with a comparatively high voltage and a small amount of double phase full wave current with a high torque and with a remarkably reduced consumption of electric power.
So far the coplanar opposed-type slotless motor using a stator coil arrangement 3 as shown in FIG. 13 has been generally employed to drive the magnetic tape in the acoustic and/or reflection apparatuses and also to drive the floppy disc in the various data processing apparatuses. Such a stator coil arrangement 3 has a number of first and second shunt coils 1,2 arranged in a common plane, the coils being generally less in number than the number of the magnetic poles provided on a permanent magnet, and moreover comparatively large spaces 4 are provided between the coils. In this case, if the number of coils is increased, the layers of coils are increased and accordingly the thickness is increased in the axial direction. As the result, the air gap is increased between the iron base plate 5 and the permanent magnet, thus reducing the density of magnetic flux to deteriorate the torque effect. Therefore in order to obtain a desired output in such a stator coil arrangement 3, it is required to increase the torque produced by each of the coils 1 and 2. This is generally attained by using a considerably thick wire as the conductors C, so that a considerable amount of current may flow through the conductors. However this will inevitably result in the dimensional enlargement of the motor and in the increase of power consumption. Such a motor has never been usable in the apparatus such as a portable video recorder operated by the dry element cells.
In order to overcome the defects and disadvantages of the stator coil arrangement 3 as shown in FIG. 13, there has been proposed another type of stator coil arrangement 8 as shown in FIG. 14. This is so called a flat and overlapped type of zigzag coil arrangement, in which a pair of zigzag coils 6,6 are arranged in combination as shown, each being composed of a group of effective conductors 6a which are alternately disposed as being overlapped with each other. This structure will actually prevent the increase of air gap provided between a permanent magnet and an iron plate of the magnetic circuit of the stator and realize a high density of magnetic flux as introduced in a publication under the title "DC Servo Motor For Mechatronics" the 3rd edition, pages 112-125 issued by Sogo Denshi (Electronics) Publisher, and a publication under the title "National Technical Report" the 26th volume, 5th issue, pages 774-782.
However this zigzag type of coil arrangement 8 still includes various defects to be further improved. Namely since the conductors C of each zigzag coil 6 are bundled together, the effective portion 6a of conductors for actually producing a torque is smaller with respect to the magnetic range defined by each magnetic pole of the permanent magnet, and on the other hand the portions 6b,6c of conductors ineffective to produce the torque are comparatively larger, and therefore the torque generation rate is lower and also the torque variation is higher resulting in the increase of power consumption. Further in case of the differential double phase full wave drive, the motor will have vibrations generated in the axial direction which may deteriorate the N and S-magnetic effects. Further in case of the sine wave drive in which the wave form of Hall generators to be employed will directly become the wave form for driving the motor, the disorder of the Hall generators, such as the variations in the DC offset and sensitivity of the Hall generators will considerably deteriorate the wow flutter. It is required to make a precise adjustment of the DC offset and sensitivity of the Hall generators in order to attain a normal performnce, as stated in the publication "National Technical Report" as mentioned above. In order to solve such a problem, the publication teaches to employ a specific, however, complex system introduced as a "current distribution double phase full wave drive system" which requires so many electronic circuits including so many elements.